1. Field of Invention
This invention relates to a polymeric composition. More particularly, this invention relates to a thermoplastic polyester resin composition.
2. Prior Art
The use of thermoplastic polyesters in various applications is, of course, well known in the prior art. Such polymers are particularly useful in the preparation of molded structures. In general, the molded structures may be prepared via injection molding, compression molding, transfer molding and the like. Depending upon the particular end use, the thermoplastic polyester may be combined with other polymers, oils, fillers, reinforcing agents, antioxidants, stabilizers, fire retardants, antiblocking agents and the like.
In general, products fashioned with thermoplastic polyester resins exhibit good rigidity, heat resistance and electrical characteristics. The molded products do not, however, generally exhibit good impact resistance. As a result, polymeric compositions comprising a thermoplastic polyester as the sole polymeric component frequently cannot effectively be used in the preparation of many molded products. Moreover, the poor impact strength has, to some extent at least, restricted the use of such polymer compositions in other end use applications.
Heretofore, several techniques have been proposed for improving the impact resistance of shaped articles fashioned from a thermoplastic polyester. In general, these methods involve the incorporation of an elastomeric polymer into a polymeric composition comprising the thermoplastic polyester. In this regard, block copolymers comprising at least one monoalkenyl aromatic hydrocarbon polymer block and at least one conjugated diolefin polymer block are known to improve the impact strength of thermoplastic polyester resin composition products. Generally, the conjugated diolefin block will be selectively hydrogenated so as to improve weatherability and heat resistance. The elastomeric block copolymer may be incorporated so as to form an interlocking network as taught in U.S. Pat. No. 4,101,605. The block copolymer may also, in effect, simply be admixed with the thermoplastic polyester as taught in U.S. Pat. No. 4,220,735. The block copolymer may also be modified by grafting an unsaturated carboxylic acid or a derivative thereof onto the block copolymer before physically admixing the same with the polyester as taught in U.S. Pat. No. 4,657,970. The thermoplastic polyester resin compositions obtained via physical admixture of the components are, however, frequently, not stable and phase separation often occurs between the polyester and the block copolymer.
While the incorporation of an elastomeric block copolymer or a modified derivative thereof into a thermoplastic polyester resin composition frequently leads to the production of a product having improved impact strength, the amount of block copolymer required is frequently relatively excessive. The improved impact resistance is, then, frequently obtained at the expense of other desirable properties characteristic of thermoplastic polyester resin products. Moreover, the selectively hydrogenated block copolymers are relatively expensive. As a result, even when the selectively hydrogenated block copolymers are used as a modifier in a thermoplastic polyester resin composition, they frequently are not used at a high enough concentration to yield a maximum impact strength. The need, then, for an improved modifier composition for use in thermoplastic polyester resin compositions which will be effective at lower concentrations and not subject to phase separation is believed to be readily apparent.